Black spent most of the mid- and late-1990s in relative obscurity, frequently playing offbeat sidekick characters. That all changed in 2000, however, with the release of High Fidelity, Stephen Frears's hilarious adaptation of the Nick Hornby novel. Black, who played a music-store clerk with an unlimited reserve of music trivia, stole many scenes from star John Cusack. Saving Silverman, co-starring Steve Zahn, followed the breakout role, though the film was a critical and commercial flop. Black made his debut as the leading man in the Farrelly Brothers' romantic comedy Shallow Hall (2001), opposite Gwyneth Paltrow. He played the superficial title character who fell for Paltrow's 300–pound Peace Corps volunteer after being hypnotized to only see inner beauty.

Black, a dual-career entertainer, has earned a cult following for his comic rock band Tenacious D, which he calls “a Smothers Brothers for the Dungeons and Dragons misfits set.” He formed the group in 1994 with guitarist Kyle Gass. They were members of Los Angeles' Actors' Gang, a troupe organized by Tim Robbins. Black made his stage debut in the group's production of Carnage. Black and Robbins also collaborated in the films Bob Roberts (1999), Dead Man Walking (1995), and Cradle Will Rock (1999).

Jack Black is a stage name. The actor has long refused to reveal his real name.